As emissions from internal combustion engines have become more of a focus for engine manufacturers, an increasing number of designs use NOx adsorbers, also known as a Lean NOx trap (“LNT”), in the exhaust path of the engine. The NOx adsorber adsorbs some of the NOx created in the combustion process, thereby reducing the amount of NOx released into the atmosphere.
The known NOx adsorbers, however, have a tendency to fill up in a relatively short period of time; sometimes as quickly as a few minutes. One technique that counters this degradation is the periodic regeneration of the NOx adsorber, commonly implemented by running the engine in a rich condition for a predetermined period of time. Because most engines today are lean burn engines, however, while the NOx adsorber is regenerating in this rich condition, additional fuel is being used. This correlates to a reduction in the gas mileage/fuel economy for the engine. Due to the high frequency of regeneration, this reduction can equate in some operating conditions to be as large as approximately 4%. To put this in perspective, many engine manufacturers today consider an improvement in fuel economy of tenths of a percent to be meaningful.